The Federal Motor Carrier Safety Administration refused last week to make changes to a regulatory guidance document it published last year allowing some specialty truck drivers at oil and gas exploration sites to extend their workdays.

FMCSA said the hours-of-service exception cannot be used by drivers hauling sand and water.

In the Aug. 12 notice published in the Federal Register, FMCSA said that after opening the issue to public comment and holding hearings, it will not change its interpretation that the waiting-time exception for oil-field workers can apply only to specially trained drivers with specially constructed equipment.